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R0 Basic Reproduction
About R0 Basic Reproduction
The basic reproduction number R0 pronounced R naught is a central concept in infectious disease epidemiology. R0 represents the average number of secondary infections produced by one infected individual in a fully susceptible population. R0 values vary by disease: measles has the highest R0 of 12 to 18, polio 5 to 7, smallpox 3.5 to 6, COVID 19 original approximately 2 to 3, Delta approximately 5 to 8, Omicron approximately 8 to 10, seasonal influenza approximately 1.3, and Ebola approximately 1.5 to 2.5. When R0 is less than 1, an epidemic dies out. When R0 is greater than 1, an epidemic grows exponentially. The effective reproduction number Re accounts for population immunity and interventions. Herd immunity threshold is approximately 1 minus 1 over R0. For measles with R0 of 15, approximately 93 percent immunity is needed. Understanding R0 is essential for vaccination target setting and intervention planning.
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